1. Field of the Invention
The present invention relates to a supporting apparatus for supporting a pinion shaft in a rack-pinion power transmitting system. Such supporting apparatus is disposed between a steering wheel shaft and an input shaft of a steering gear which are not arranged on the same straight line (i.e., arranged in an inclined or helix relation) and serves to support a pinion shaft of the steering gear which transmits the rotational force received from the steering wheel shaft to a pinion gear.
2. Related Background Art
In the past, a steering system of a motor vehicle has been designed as shown in FIG. 3.
An end of a steering wheel shaft 102 rotated around its own axis by manipulating a steering wheel 100, and an input shaft 108 of a steering gear 106 for shifting a tie-rod 104 a an axial direction are interconnected via a connecting shaft 110. The ends of the connecting shaft 110 are respectively connected to one end of the steering wheel shaft 102 and to one end of the input shaft 108 via universal joints 112, 114 such as cross joints. Thus, the rotational force from the steering wheel shaft 102 is transmitted to the input shaft 108 of the steering gear 106 through one of the joints 112, connecting shaft 110 and the other of the joints 114.
The details of the steering gear are shown in FIG. 4. The steering gear 106 comprises a rack shaft 122 having a rack 121 and axially slidably (in a direction perpendicular to the plane of FIG. 4) inserted into a housing 120, a pinion shaft 124 rotatably inserted into the housing 120, a pinion 136 fixedly mounted on an intermediate portion of the pinion shaft 124 and meshed with the rack 121, and a pair of ball bearings 126 disposed between an inner surface of the housing 120 and an outer surface of the pinion shaft 124 on both sides of the pinion 136 to support supporting portions 125, 127.
Both ends of the rack shaft 122 and one end (right end in FIG. 4) of the pinion shaft 124 which is not meshed with the rack 121 are protruded from the housing 120, respectively, so that, by rotating the protruded end of the pinion shaft 124 (corresponding to the aforementioned input shaft 108), the protruded ends of the rack shaft 122 can be displaced in the axial direction. In this way, the rotational movement is converted into linear movement.
In such a construction as just described, the rigidity of the pinion shaft 124 to the load acting in the axial direction (left-and-right direction in FIG. 4) greatly influences the response characteristic of the power transmission between the pinion shaft 124 and the rack shaft 122. Thus, in the past, ball bearings of angular type or tapered roller bearings have been used as the pair of bearings 126, and the both bearings 126 were appropriately pre-loaded in assembling the pinion shaft 124 into the housing 120. However, this solution makes the assembling of the pinion shaft 124 into the housing 120 difficult and also makes the rack-pinion power transmitting system such as the steering gear 106 expensive.
In order to improve the assemblage of the pinion shaft 124 into the housing 120, conventionally, as shown in FIG. 5, it has been known to support the pinion shaft 124 at its inner end by a roller bearing such as a needle bearing 128 and at its intermediate portion by a deep groove ball bearing 130. However, with this arrangement, the rigidity of the pinion shaft 124 to the load acting in the axial direction is weaker than that of the arrangement of FIG. 4, thus not always providing a sufficient response characteristic of the power transmission between the pinion shaft 124 and the rack shaft 122.